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A2A Client

Use the ra2a client to discover agents, send messages, and stream responses.

Installation​

cargo add ra2a --features client

Discover an Agent​

Every A2A agent publishes an Agent Card. Use the client to fetch it:

use ra2a::client::{A2AClient, Client};

let client = A2AClient::new("https://agent.example.com")?;
let card = client.get_agent_card().await?;

println!("Name: {}", card.name);
println!("Skills: {:?}", card.skills);

Send a Message​

use ra2a::types::Message;

let message = Message::user_text("What is the weather in Tokyo?");
let mut stream = client.send_message(message).await?;

while let Some(event) = futures::StreamExt::next(&mut stream).await {
    match event? {
        // Handle task updates, artifacts, etc.
        event => println!("{:?}", event),
    }
}

Get a Task​

Retrieve a previously submitted task by ID:

let task = client.get_task("task-id-123").await?;
println!("Status: {:?}", task.status.state);

Cancel a Task​

let task = client.cancel_task("task-id-123").await?;
println!("Canceled: {:?}", task.status.state);

SSE Streaming​

The client automatically handles Server-Sent Events (SSE) streaming. When you call send_message, the response is streamed as a series of events:

  • TaskStatusUpdate — the task's state changed
  • TaskArtifactUpdate — a new artifact (text, file, etc.) was produced
  • TaskComplete — the task finished

Error Handling​

use ra2a::error::Error;

match client.send_message(message).await {
    Ok(stream) => { /* process stream */ }
    Err(Error::Transport(e)) => eprintln!("Network error: {e}"),
    Err(Error::Protocol(e)) => eprintln!("Protocol error: {e}"),
    Err(e) => eprintln!("Other error: {e}"),
}
  • Server — build an A2A agent
  • Storage — configure task persistence